DESCRIPTION: This AREA grant application is designed to test the hypothesis that H. pylori or its derived cytotoxin may induce toxic manifestations through the enhanced production of reactive oxygen species (ROS). Preliminary studies from the P.I.'s laboratory have shown an increased production of ROS by, and DNA damage in, human gastric adenocarcinoma cell lines in association with H. pylori cells. Furthermore, these studies demonstrated that H. pylori strains which possess very high levels of an 87 kDa cytotoxin-associated activity produce more ROS in these cell lines compared to H. pylori strains in which the cytotoxin gene has been disrupted. These observations were recently confirmed in isolated and cultured gastric cells from H. pylori negative endoscopic biopsies. The specific aims of this proposal are: 1) Assess the in vitro generation of various ROS, including superoxide anion and hydroxyl radical, in cultured normal human gastric cells and in H. pylori cells. 2) Further identify the ROS which are involved in H. pylori-induced gastric damage. 3) Determine the relative roles of the enzyme systems xanthine oxidase, microsomal cytochrome P450, NADPH oxidase and mitochondria-specific succinate dehydrogenase in the production of ROS in cultured normal human gastric cells following inoculation with H. pylori or its derived cytotoxin.